1. Field of the Invention
The present invention is directed generally to a buffer and, more particularly, to a buffer with adjustable slew rate and a method of providing an adjustable slew rate.
2. Description of the Background
Slew rate is a ratio of a rise or fall in voltage to the amount of time that rise or fall takes. Consequently, slew rate is a quantity which can be a controlling factor in the performance characteristics of a device. A device having a low slew rate can degrade the performance and speed of a system containing the device, while a device having a high slew rate may not allow the system to react to changes in the state of the device, and thereby cause breakdown of the system.
Those effects of slew rate have led manufacturers of processors and computer systems, such as Intel, to specify performance windows into which device slew rate characteristics must fall in order to properly operate with their processors and computer systems. However, process variations between different fabrication processes can cause large variations in device characteristics, such as drain to source current. For example, drain to source current characteristics for a p-channel fabrication have been shown to vary as much as 48%, depending upon the manufacturing process used to create the device. Such variations in device characteristics make it difficult, if not impossible, to insure that a device will exhibit slew rate characteristics within the performance window as set forth by the computer manufacturer.
Therefore, the need exists for a buffer that allows adjustment of slew rate characteristics after a circuit or device has been manufactured.